Botensilimab (Fc-enhanced anti-cytotoxic lymphocyte-association protein-4 antibody) Plus Balstilimab (anti-PD-1 antibody) in Patients With Relapsed/Refractory Metastatic Sarcomas.

Purpose: Outcomes for patients with advanced sarcomas are poor and there is a high unmet need to develop novel therapies. The purpose of this phase I study was to define the safety and efficacy of botensilimab (BOT), an Fc-enhanced anti-cytotoxic lymphocyte-association protein-4 antibody, plus balstilimab (BAL), an anti-PD-1 antibody, in advanced sarcomas.

Methods: BOT was administered intravenously (IV) at 1 mg/kg or 2 mg/kg once every 6 weeks in combination with BAL IV at 3 mg/kg once every 2 weeks for up to 2 years. The primary end point was to determine dose-limiting toxicities during the dose-escalation period. Secondary end points include objective response rate (ORR), duration of response (DOR), disease control rate, and progression-free survival (PFS) by RECIST 1.1. Exploratory end points include assessing patient biomarkers including tumor mutational burden, cytokines, and PD-L1 expression.

Results: Overall, 64 patients with sarcoma were treated; all were evaluable for safety and 52 for efficacy. The most common treatment-related adverse event (TRAE) was diarrhea/colitis occurring in 35.9% of patients, with grade 3 in 6.3% of patients. No grade 4 or 5 TRAEs were reported. For all evaluable patients, ORR was 19.2% (95% CI, 9.6 to 32.5), and 27.8% (95% CI, 9.7 to 53.5) for evaluable patients with angiosarcoma (n = 18); 33.3% in visceral and 22.2% in cutaneous subtypes. Median PFS for evaluable patients was 4.4 months (95% CI, 2.8 to 6.1), with a 6-month PFS rate of 36% (95% CI, 22 to 50) and a median DOR of 21.7 months (95% CI, 1.9 to not reached).

Conclusion: The combination of BOT/BAL demonstrated promising efficacy and safety in a large cohort of heavily pretreated sarcoma patients. This encouraging activity warrants further investigation (ClinicalTrials.gov identifier: NCT03860272).